Foreign Fish Feel At Home Here

ENVIRONMENT

Area's Extensive System Of Canals Helps Protect Them

February 10, 1996|By NEIL SANTANIELLO Staff Writer

Among Florida's non-native invaders, melaleuca, Australian pine and Brazilian pepper are practically household names. Lesser known than those pest plants, though, are another group of exotics that also flourish in South Florida's hospitable sub-tropical climate.

They have names like black acara, firemouth cichlid, red-striped eartheater and blue tilapia. Those exotics are among 18 species of non-native fish introduced to and thriving in Florida canals and lakes. Sixteen of those, including walking catfish, live in South Florida waters.

Imported from Asia, Africa and South America, all have either been accidentally or deliberately released into South Florida waters by aquarium owners and possibly fish farms, said Paul Shafland, director of the Florida Game and Fresh Water Fish Commission's Nonnative Fish Research Laboratory in Boca Raton.

Since exotic fish are accustomed to warmer temperatures in tropical countries, they are often the first found floating belly-up in canals after a severe cold snap, Shafland said.

But many are able to escape death as cold fronts roll through thanks to the region's network of manmade flood-control canals, he said.

The larger, deeper canals in Broward, Dade and south Palm Beach counties are cut into the Biscayne aquifer, a water table located less than 10 feet below the earth's surface in some places, Shafland said.

That groundwater, in the winter, is warmer than water in natural lakes and marshes. It flows into deeper canals and makes them "thermal refuges" for exotic fish, Shafland said.

Major canals generally can run 12 to 15 feet deep but some have depths 25 or 30 feet, he said.

"That's one reason why these canals hold so many exotic fish and why they are so successful," he said. "It's not so much they have the ability to outcompete native fish."

Shallow, natural waterways, on the other hand, have temperatures regulated mainly by drops and rises in atmospheric temperature, Shafland said. In Everglades conservation areas, water depths can range from one to two feet or less.

One example is Lake Okeechobee, Florida's most renowned freshwater fishing hole. When cold winds blow across the shallow saucer-shaped lake it whips up waves that churn air and water together, he said.

So the lake temperatures approach air temperature more quickly than surrounding canals, he said.

Rows of houses and trees that line canals in urban areas also provide wind breaks that help keep their waters warmer, he said.

"If we had set about to design a habitat receptive for tropical exotic fishes, we could not have designed a freshwater system better than these canals in coastal South Florida," he said.

Though Florida's cold fronts can reduce exotic fish populations, they won't wipe them out entirely in South Florida, Shafland said.

Still some exotic fish are more sensitive to cold than others. Water temperatures that drop below 60 degrees can affect the butterfly peacock. Oscars are in trouble at temperatures lower than 55, and spotted tilapia at temperatures lower than 50.

Forty-degree-or-below water can harm all exotics, Shafland said.

The first exotic fish appeared in South Florida around the mid-1950s, Shafland said. The latest exotic invader is the jaguar guapote, a fish native to Central America, that turned up four to five years ago in Dade County, he said.

"Once they become self-perpetuating, there's no way we can eliminate them," he said. One of Florida's 18 exotic fish species was released deliberately by the Game Commission, and its inability to survive cold played a role in that introduction.

That fish, the butterfly peacock, is a world-class sport fish from South America. The Commission stocked it in Dade and Broward canals from 1984 to 1987 to control climbing populations of another exotic fish, tilapia, and to introduce another sportfish into urban areas to improve recreational fishing there, Shafland said.

The fish feeds on tilapia.

Biologists knew their introduction could not get out of hand. Peacocks are so cold-sensitive they can only survive in deeper, warmer coastal canals, Shafland said.

Populations in small ponds will die with the first cold winter, Shafland said.